Or it could mean that, other than April's filming, there was no other Doctor Who
filming planned for this spring. Since he had a hole in his schedule, he could take another job, not unlike Cumberbatch and the Julian Assange film.
You're right, it doesn't mean that Matt Smith is leaving. This does, however, make it unlikely that we'll see more Who
in 2013 than what was announced at Toy Fair as season eight wouldn't begin filming before July-ish.